The present invention generally relates to a system for correcting spinal deformities anteriorly. More specifically, the present invention relates to an improved anterior transpedicular fixation system and a method for maintaining vertebrae in a desired symmetrical spatial relationship.
Various forms of instrumentation and procedures are known for surgical treatments of spinal disorders, burst fractures, or tumors. For example, Harrington posterior Spinal Instrumentation, Edwards Hooks and Rod Sleeves, Luque Segmental Spinal Instrumentation and Luque Rectangles, and Kostuik-Harrington Instrumentation are commonly used. U.S. Pat. Nos. 4,433,676; 4,653,481; 4,269,178; 4,409,968; and 4,648,388 disclose details of such instrumentations. Some of the above systems utilize hook-type members which are merely hooked over the laminae or on selected transverse processes of the spine. Other systems, such as the Luque Segmental Spinal Rectangles which is used to stabilize spinal fractures and low back fusions, use Luque wires to secure the rectangle to the spine.
In some of the prior posterior spinal fixation systems, screws are used to hold a single rod in place. In other systems, screws are used to hold a slotted plate in place. The screws and slots are located so that the plate can be adjusted in order to align the plate apertures or slots with the end of the screw. Typically, a nut is used to hold the plate to the screw. The latter arrangement is also referred to as a Steffee plate, which is a posterior fixation system with the cantilever arrangement. Such a arrangement has the large moments applied to the plate and screw junction, but has little purchase between the plate and the screw and nut since only a small portion of the plate is engaged adjacent to the slots. In addition, the rigid plates is not flexible in locating the fasteners in the vertebrae. The above posterior approaches, even to this level of advancement, do not solve the problem of treating thoracolumbar tumors or burst fractures.
In the early 1980""s various anterior fixation devices were developed to allow visualization of bone fragments that were present with burst fractures, so that attention could then be directed toward complete decompression of the canal to provide the best environment for neurological recovery. However, the anterior approach has caused increased operative morbidity due to the very difficult nature of the procedure. Moreover, many of the anterior fixation approaches have problems of potential risk to the vascular network and in complete clearance of the spinal canal. The conventional anterior approaches are not true anterior fixation but anteo-lateral fixations. Most of the anterior systems rely on support from the vertebral body only and therefore cannot be used in the extremely osteoporotic spine because the vertebral body strength is not sufficient.
One such system is the Kanada device marketed by Acromed, Inc. of Cleveland, Ohio. The Kanada device utilizes vertebral body staples through which fixation screws are placed into the vertebral body. Rods are then engaged between the screws in the superior and inferior vertebral bodies. Normally two screws are placed in each body. Therefore two rods are needed between the vertebrae. The rods are threaded at their ends to allow compression and distraction. However, the loads are born solely by the vertebral bodies. The posterior column of the spine or pedicle do not share any loads.
U.S. Pat. No. 4,289,123 discloses another anterior spinal fixation system, marketed by Zimmer, for treating tumors or thoracolumbar burst fractures. This system is similar to the Kanada device in that it uses rods between the superior and inferior vertebrae. In addition, a pair of large plates are contoured in accordance with the vertebrae and engage with the same through, such as screws.
Several plating systems have been developed for anterior internal fixation of the spine. Among these plating systems, the Syracuse I-plate provides a number of differently sized I-shaped plates which are engaged across the burst fracture. However, the Syracuse I-plate does not allow for compression or distraction of a bone graft between the superior and inferior vertebrae. The Stafix plating system, provided by Duma International of Taipai, Taiwan, includes a plate that has a number of screw holes and a single screw slot. The Stafix plate permits quadrilateral placement of bone screws, but not compression or distraction. Moreover, the Stafix plate, as with the above-mentioned anterior plates, can not provide rigid or semi-rigid fixation using bone screws or bone bolts. Moreover, U.S. Pat. No. 5,324,290 discloses an internal anterior fixation systems for treating vertebral burst fractures. The internal anterior fixation system uses an elongated plate which includes integral superior, inferior and bridge portions. The superior and inferior portions are provided for fixation to corresponding vertebrae while the bridge portion spanning between the portions over the affected vertebra.
Therefore, it is an object of the present invention to provide a fixation system that is capable of efficient management of thoracolumbar burst fractures and tumors and of easy implantation, to thereby reduce operative morbidity. Another object is to provide a system which permits anterior load sharing by the fixation system, posterior load sharing by posterior vertebral structure. Yet another object is to provide a fixation system that has compression and/or distraction function.
The present invention relates to an anterior transpedicular fixation system having longitudinal and transverse support members. The support members are connected to each other and mounted onto one or more vertebrae to support the spine and to prevent rotational or translational movement of the support members. The anterior transpedicular spinal fixation system allows a surgeon the full access to the disc area, captures two cortical surfaces via transpedicular screws or rods insertion, and pulls the two vertebral bodies closer to each other insuring a tight fusion. Therefore, the anterior transpedicular spinal fixation system is capable of distributing compressive loads to the support members, the vertebral body, and the posterior column of the spine, restraining the support members from rotational and translational movement, and preventing displacement of the graft material.
In one embodiment, the anterior transpedicular fixation system comprises a pair of supporting plates each having a first engaging portion, a second engaging portion, and a bridge portion integrally spanning between the first and second engaging portions. The first and second engaging portions each define a receiving portion, such as an opening. Moreover, a plurality of fixation elements are provided each adapted to extend through one the openings and be mounted onto a vertebra. Further, the anterior transpedicular spinal fixation system comprises a joining member adapted to connect the bridge portions of the supporting plates. It is preferred that the components of the anterior transpedicular spinal fixation system are made of rigid materials. As a result, the supporting plates are restrained from rotational or translational movement. In an alternative embodiment, the bridge portions of the supporting plates and the clamping member are merged into one unitary member to provide both longitudinal and transverse support to the spine.
The present invention also relates to a method for maintaining vertebrae in a desired relationship. The surgical process according to the present invention includes removing the patient""s intervertebral disc or vertebral body, inserting the bone graft material to replace the extracted anterior column, pre-drilling pilot screw holes on both cordices of the pedicle and the vertebral body, and mounting a support member to the vertebral body to increase its mechanical stability and to distribute rotational and translational loads to the support members, the vertebral body, and the posterior column of the spine.
These and other features and advantages of the present invention will be readily apparent from the following detailed description of the invention, the scope of the invention being set out in the appended claims.